Radiant tube furnace



' loi Patented Mar. 12, 1940 PATENT LOFFICE 2,193,362 RADIANT TUBE'FURNACE James C.'Woodson, Cleveland, Ohio, assignor to Lee Wilson SalesCorporation, Cleveland, Ohio,

a corporation of Ohio Application January 16, 1939, Serial No. 251,131

7 Claims.

This invention relates to a furnace and, in particular, to a furnaceadapted to be heated by radiation from heat-exchange tubes mountedinteriorly thereof for conducting hot combustion gases or other fluidheating medium.

Numerous types of radiant tube furnaces have been proposed heretoforeand it is the general object of this invention to improve upon suchfur-v naces as previously constructed.

The invention is concerned particularlywith a novel form ofheat-exchange tube of such construction as to provide better fueleconomy than has been obtainable with the heat-exchange tubes now inuse. A further object of the invention is to provide a tube having alonger useful life than the tubes now in use and, furthermore, toprovide a tube which may be readily fabricated at relatively low cost.y,

In a preferred form of the invention, I provide a heat-exchange tubehaving substantially parallel branches or passages and preferably mountit adjacent a wall of the furnace. To thedischarge end of the tube, Iconnect an exhaust flue embedded in the furnace wall. I also provide aconnection from the discharge end of the tube to the entrance thereof topermit a small portion of the combustion gases to be induced into thestream of freshly -burning gases for rev-circulation` therewith.

Further details of the embodiment outlined above will be explainedherebelow with reference to the accompanying drawing in which Fig. 1 isa transverse sectional view through a furnace having the inventionincorporated there- 1D;

Fig. 2 is a partial sectional view taken substantially along the planeof line II-lI of Fig. 1; and Fig. 3 is a sectional view through theheat-exchange tube alone along the plane of line III-III of Fig. 1. V

Referring now in detail to the drawing, I have l illustrated therein afurnace I of the cover type merely as a convenient example since theinvention may be applied to various types of furnace structures. Thefurnace I0 includes a cover II removably disposed on a -base or hearth,aportion `of which is shown at I2. The cover II is open at the bottomand comprises side walls, end walls and a. roof of refractory materialassembled within a structural frame I3 and sheathing plates Il. Thebase' j| 2 is built up from rey fractory material assembled on anysuitable supporting foundation. The base is adapted to support a chargeof material I5 such as a stack of vsheets or coil of strip to besubjected to process- .disposed at any convenient angle. A centrallonshortly.

ing, e. g. annealing. The base also provided with a, sealingchannel I6adapte to receive the lowerv edge of an open-bottomed protective coverIl fabricated from light plate. The base I2 also has a shoulder ormargin I8 adapted to receive the bottom edge of the side and end wallsof the cover. v

Heat-exchange tubes I9 are mounted interiorly of the furnace and mayconveniently be disposed in spaced relation along the side walls. of thecover. The tubes I9 may be of any convenient construction but I prefer atubeof substantially oval section, the lower end of which is disposedsubstantially at right angles to themain body of the tube, as indicatedat 20. This portion of `the tube traverses the furnace wall and isembedded therein.

-As shown, the tubes I9 are disposed with their longer portions 2|vertical although they may be gitudinal partition 22 disposed in eachtube divides it into a pair of substantially parallel passages orbranches 23 and 24. A cross wall 25 substantially in line with thepartition 22 divides the lower portion 20 of the tube andwith thepartition, constitutes a baie extending from the bottom of the tube to apoint spaced below the top thereof, thereby establishing communicationbetween the passages 23 and 24 at their upper ends. A 'port or opening26 is formed in the cross wall 25 for a purpose which will appear Aburner 21 extends into the side of the bottom portion 20 of the tubewhich is in communication with the passage 23. The other side of theportion 20 terminates in the side wall of the furnace and does notextend outwardly therethrough, the outervend of this portion beingindicated at 28. A spark gap igniter 29 is disposed adjacent each burnerand is connected to an energizing transformer 30. A manifold 3l extendsalong each side of the furnace for supplying to the burners acombustible mixture of air and gas.

The side of the lower portion 20 of each tube opposite that into whichthe burner 21 exten-ds, indicated at 32, has an opening 33 at the topthereof. Anrexhaust ue 34 embedded in the furnace wall fits down overthe opening 33. The exhaust ue serves to carry waste gases upwardlythrough the furnace wall and to the exterior atmosphere for discharge.This construction has a particular advantage in that the waste gasescontain a substantial amount of heat even after traversing the passages23 and 24. A portion of this remaining heat content ofthe exhaust gasesis absorbed by the brlckwork composing the furnace wall, thereby makingup at least in part, the heat lost from the exterior of the walls. i

The operation of the furnace of my invention will now be explainedbriey. It will be understood that the covers H and I1 are raised topei".- mit the charge I5 to be initially placed on the base I2. Thecovers are then replaced as illustrated. A combustible mixture suchasfuel ses and air in proper proportions is supplied to the manifolds 3|under the control of suitable valves in a' supply main and the mixtureissuing from the burners 2l is ignited by spark gaps created understood,of course, that where the furnace is employed in continuous processing,the burners remain ignited and it is necessary to energize the igniterpoints only when starting up.

After ignition, the combustible gases burn as they traverse the passages23 and 24. After passing around the upper end of the partition 22 anddescending through the passage 24, the combustion gases having given outmost of their heat to the walls of the' tubes I9, enter the portions 32of the lower ends of the tubes and thence pass upwardly through theopenings 33 and through the exhaust hues 34. A small portion of thecombustion gases which have traversed the passages 23 and 24 is inducedthrough the opening 26 in the cross Wall 25 into the stream of freshlyburning gases ascending from the burner through the passage 23. Thisre-circulation of a portion of the combustion products tends toeliminate substantial differences between the temperatures of differentparts of the tube by cooling the gases slightly in the initial stages ofcombustion. This reduces erosion of the tube in the area on which theflame jet impinges and thereby lengthens the useful life of the tubes.As previously pointed out, as the combustion gases ascend through theexhaust flue 34 they give up a certain portion of their heat to thefurnace walls, thereby making up at least in part, the heat lost fromthe exterior of the walls, and increasing the overall thermal efficiencyof the furnace. It will be noted that while the shape of the iiues 34 insectionis different from that of the passages 23 and 24, the dimensionsare such that the sectional areas are approximately the same at allpoints along the path of the gases.

After the charge I5 has been heated to the proper temperature, the coverIl is removed and disposed on another previously loaded base, the coverl1 being left in place to protect the charge during the slow coolingthereof.

It will be apparent from the foregoing description and explanation thatthe invention provides a radiant tube furnace having numerous advantagesover furnaces of this type previously available. In the rst place, arelatively long path is afforded for the combustion gases whichincreases the amount of heat given out by them to the surroundingheat-conducting walls of the tube. Re-circulation of a portion of thecombustion gases tends to make the temperature of all portions of thetube substantially uniform.

The economy obtained by leading the exhaust pre-mixed'airand gas whichalso contributes to a high thermal efiiciency.

Although I have illustrated and described but a single preferredembodiment of the invention,

:incassa it will be understood that Anumerous changes and modificationstherein may be made without departing from the spirit of the inventionor the scope of the appended claims.

I claim: e

1. In a furnace having a side wall and a roof, a heat-exchange tubedisposed substantially vertically adjacent said wall, said tube beingsubstantially oval-shaped in section and having a baie extendinglongitudinally therethrough providing a pair of substantially parallelgas passages and having a portion at its lower end disposedsubstantially at right angles to the remainder of the tube, said portionextending into said wall, and an exhaust ii`ue extending upwardly withinsaid wall from the lower end of said tube and communicating with one ofsaid having a portion at its lower end disposed sub` stantially at rightangles to the remainder of the tube, said portion extending into saidwall, and an exhaust fiue embedded in said wall and extending upwardlytherein, said flue communieating with one of said passages at the lowerend of the tube.'l

3. In a furnace having a side wall and aroof, a heat-exchange tubedisposed substantially vertically adjacent said wall, said tubeproviding a pair of substantially parallel gas passages and having aportion at its lower end disposed substantiallyvat right angles totheremainder of the tube, said portion extending into said wall, one ofsaid passages terminating within the wall and being open at the topwhereby it communi` prising a plurality of heat-exchange tubes mountedinteriorly of said cover, each tube comprising a .burner portionextending through the cover below the top of said base when the cover ispositioned thereon and adapted to receive a burner therein, a verticalheat-exchange portion extending upwardly from said burner portion, asecond heat-exchange-portion substantially parallel to the first andcommunicating therewith at the upper end thereof, an outlet portioncommunicating with the lower end of said second heat-exchange portionand extending outwardly therefrom below the top of said base when thecover is positioned thereon, and a stack communicating with each outletportion and extending upwardly therefrom.

5. In a furnace including a cover having side walls and a roof and abase, a heat-exchange tube disposed substantially vertically adjacentsaid wall, said tube providing a pair of substantially parallel gaspassages and having a portion at its lower end disposed substantially atright angles to the remainder of the tube, said portion extending intosaid wall below the top of said `base when the cover is depositedthereon,k

and an exhaust ue extending upwardly along said wall from the lower endof said tube and communicating with one of said passages.

' 6. In a furnace having aside 'wall and a roof, a heat-exchange tubedisposed substantially vertically adjacent said wall, said tube beingsubfio stantially oval-shaped in seotion and having a baille extendinglongitudinally therethrough, providing a pair of substantially parallelgas pas? sagesV and having a portion at its lower end disposedsubstantially at right. angles to the remainder of the tube, saidportion extending into said Wall, an exhaust ue 'extending upwardlyalong said Wall from the lower end of said tube and communicating withone of said passages, and a burner extending into the other passage,said baille having a bleeder port adjacent said burner. y

7. In a furnace having a sidewall and a roof, a heat-exchange tubedisposed substantially vertically adjacent said wall, said ltubeproviding a pair of substantially parallel gas passages, a burnersupplying combustion gases to one of said passages, and an exhaust vueconnected to the other passage at. the lower end of said tube andembedded in said wall.

